No, the sentence is not correct because of the incongruity in verb tenses:
Though Jerry is too shy, he walked out on stage as cool as cucumber and sang like he had been doing it all his life.
Whether Jerry is shy (now or by nature) has no bearing on how he performed in that particular moment in the past. More importantly, Jerry may not be shy now, but he certainly was shy at that point in time.
Another minor problem in the sentence is the missing article for "cucumber".
After all these fixes, your sentence should read as follows:
Though Jerry was too shy, he walked out on stage as cool as a cucumber and sang like he had been doing it all his life.
Note that claiming "Jerry was too shy" does not at all imply that he is no longer shy. Rather, all we're saying is that during that point in time, he was shy.